1. Field of the Invention
This invention relates to improvements in a high-speed dobby. By reducing the number of mover members required for moving the keys which control the rocking movement of the main dobby crank arms and for locking said main crank arms in position, and hence reducing the inertial mass in play, and in addition by operating said mover members by a single control device operating on only one side of the main crank arms and situated in the most accessible region of the dobby, and moving them only during the pauses in the rotation of the drive shaft imposed by the modulator, result not only in a considerable cost reduction and ease of maintenance, but also in higher speeds as required by modern air and water looms together with considerable reliability and extreme safety even in the case of random malfunction of the controls. In addition there is an increase in the time available for the execution of said controls and it becomes possible to achieve reverse running from any angular position of the drive shaft without the need to use additional members.
More specifically, the invention relates to new key mover mechanisms which are extremely simple and functional, each consisting substantially of two single opposing keying levers pivoted on the cam of the crank arm, they cooperating at one end with the relative key and at their other end with a single control device. The invention also relates to a particular control device comprising two identical cam systems operating alternately at each half-revolution of the dobby drive shaft on a single operating unit composed of two pushers of different travel strokes for respectively locking the cam and extracting the key by acting on one of said two opposing keying levers of the key mover mechanisms.
2. Description of the Related Art
In rotary dobbies each main crank arm is mounted idly on the drive shaft via a cam which is interposed between the shaft and the big end of the crank arm, to be rigidly connected by a key to said crank arm or to said shaft, which moves with intermittent motion in the form of 180.degree. rotations followed by a pause, the key being movably supported by said cam and being urged during said drive shaft pauses by mechanical movement means such that one of its ends engages one of two opposing radial grooves provided in the big end of the main crank arm or one of two opposing radial grooves provided in the drive shaft. Various types of key mover mechanisms for a rotary dobby are known from the state of the art.
In the construction described in European Patent appln. publication No. 0 466 234 of Jan. 15, 1992 by the present applicant, said mechanism consists substantially of an elliptical control ring mounted coaxial to the dobby drive shaft and inserted into a suitable transverse groove provided in the key body, said ring being fixed on an operating lever which has always to be repositioned in its central rest position by a complex elastic system and has its fulcrum in a region which is not easily accessible.
Although such a construction has the advantage of being able to be operated by a single control device located on only one side of the main crank arm, it has however various drawbacks the main one of which derives from the considerable moving masses which generate intense inertial forces and hence necessitate corresponding greater control forces with the consequent need for more costly and complicated structures. A further drawback is the difficulty of mounting the unit comprising the main crank arms, the ring control levers and the elastic reaction systems. Said drawbacks are attenuated in other key mover mechanisms known in the art in which a single lever rigid with the key and hinged to the cam is used (see for example U.S. Pat. No. 4,544,000 or European patent application 239,514, both by Staubli). These latter have however the drawback of requiring a control device which has to act in two opposing positions about the dobby drive shaft, which in addition to constructional and assembly complications makes it necessary to effect the movements outside the pauses in the rotation of the drive shaft, with consequent reduced reliability.